Polymer dispersions are well known as binders in the production of coating compositions such as plasters, renders, adhesives, and paints. Advantages of using water borne systems for paints include low cost, ease of application and cleanup, reduced drying times, and low or no odor or emissions of volatile organic compounds (VOC). For interior paints, where good mechanical properties at low binder content are required, wet scrub resistance (WSR) is a critical performance criterion.
To obtain good WSR in emulsion based interior paints, various proposals are described. For instance, U.S. Pat. No. 6,624,243 describes an aqueous dispersion that comprises a hydrolyzable silane compound in combination with glycidyl methacrylate. The hydrolyzable silane compounds include ethylenically unsaturated silane monomers or other reactive silane compounds such as mercapto-, epoxy-, and amino-silanes. EP0327006 describes the use of ethylenically unsaturated silane monomers to improve WSR of low emission interior paints. In addition, EP0640629 describes a polymer modification of carboxylated polymers with epoxy silanes. The silane functionality can be introduced during or after polymerization. EP0327376 discloses a copolymer dispersion that includes a silicon compound having an additional reactive group, for example, a mercapto group, which will be incorporated by a free radical mechanism, or an oxirane, which may react with a carboxyl group of, for example, an acrylic acid comonomer. Preferably the reactive group is an ethylenic double bond.
Besides higher production costs, the functionalized siloxane compounds suggested in the prior art can lead to undesirable side effects. Mercapto groups can reduce the molecular weight of the coating composition by acting as a chain transfer agent. Epoxy groups can lead to reduced storage stability by interactions with other formulation components like for example acrylic thickeners Amino groups can lead to yellowing and affect the pH of the coating composition.
There is therefore a continued need for polymer-based aqueous binder systems that exhibit improved wet scrub resistance.